The following definitions are provided to facilitate an understanding of the invention.
The term "target" or "target molecule", in a diagnostic sense, refers to a molecule of interest, i.e. the molecule whose presence one wants to know. This application uses the term "signal nucleic acid" to refer to the target, if such target is present in sufficient quanities to produce a measurable response. However, the term "signal nucleic acid" also refers to nucleic acid that may be generated in the presence of target. By way of example, without limitation, signal nucleic acid may be generated in the presence of non-nucleic acid targets or nucleic acid targets through nucleic acid amplification reactions such as polymerase chain reactions (PCR) and RNA-dependent RNA polymerase reactions, such as Q-Beta replicase.
Nucleic acid antibody reactions are characterized by processes which are called SELEX (NexStar Pharmaceuticals, Inc., Boulder CO). These processes describe the manner in which nucleic acids may be selected for affinity to non-nucleic acid targets, such as proteins and other molecules of interest. The selected nucleic acids can be used as ligands for affinity reactions in the manner similar to antibodies.
Nucleic acid hybridization reactions are based on the affinity exhibited by complementary strands of nucleic acid. Nucleic acid target molecules can be identified by the binding of such target to a complementary ligand nucleic acid.
Assays based on nucleic acid antibodies and nucleic acid hybridization tend to be time consuming and complex. There exists a need for photo-electrochemical detection of signal nucleic acid.